Traditional printing devices rely on a mechanically operated carriage to transport a print head in a linear direction as other mechanics advance a medium in an orthogonal direction. As the print head moves over the medium an image may be laid down. Portable printers have been developed through technologies that reduce the size of the operating mechanics. However, the principles of providing relative movement between the print head and medium remain the same as traditional printing devices. Accordingly, these mechanics limit the reduction of size of the printer as well as the material that may be used as the medium.
Handheld printing devices have been developed that ostensibly allow an operator to manipulate a handheld device over a medium in order to print an image onto the medium. However, these devices are challenged by the unpredictable and nonlinear movement of the device by the operator. The variations of operator movement, including rotation of the device itself, make it difficult to determine the precise location of the print head. This type of positioning error may have deleterious effects of the quality on the printed image.
One navigation solution for a handheld mobile printer uses 1 or 2 navigation sensors (such as optical mouse sensors) that have position accuracy errors related to the accuracy of the sensor and the inherent sensor error associated with the distance travelled during the printing process. Secondarily, the printing device can not be lifted from the print medium without losing position information, and can not reacquire absolute position information when returned to the print medium. This navigation solution uses optical or laser navigation sensors with plain or unmarked paper. These navigation sensors determine X, Y position data relative to the actual motion that is taking place on the print medium. They often have a high degree of accuracy for small amount of motion (travel), but position errors generally accumulate over larger motion (such as is required to produce a printed image). These position errors can not be filtered out or reset. Position errors become cumulative over time. As part of the position determination process, this solution also requires a configuration of two sensors that each provide absolute X, Y position data that is then used to calculate the required angular accuracy for the print head position that is required to support printing.
A second handheld mobile printer navigation solution uses pre-tagged paper, which has many advantages that can contribute desirable qualities of Print Quality (PQ) such as absolute position information that can be encoded on the paper, therefore eliminating cumulative position errors and allowing the handheld printer to be lifted from the paper, which provides improved user friendly flexibility. This second solution for the handheld mobile printer uses pre-marked (pre-tagged) paper using a marking technology that is not visible to the human eye such as yellow or infrared on the paper medium. This pre-tagged media/paper has encoded on its surface accurate absolute X, Y position information relative to the actual position that the data was encoded on the media. To decode or determine the position data, this solution uses different sensors that can read the encoded information to extract the absolute X, Y position data. The solution uses “CMOS imaging sensors” (IR Cameras) tuned to the light wave of the encoded marking that then can read the absolute encoded X, Y position information on the media while the handheld printer is in motion. The solution allows the handheld printer to extract absolute position for each position measurement. Position errors are not cumulative. As with the optical navigation (mouse sensors) technology, this solution again requires a configuration using two sensors that each provides absolute X, Y position data that is then used to calculate the required angular accuracy for the print head position that is required to support printing.